Needmo two battery recommendations.

[tnq5546]

Bought a used boat with a 50 hp motor and two batteries. A group 24 which I thought was for starting, and I replaced the group 27 with a group 31 for all my accessories. It turns out that the only thing being powered by the group 31 is the trolling motor. The boat has a stereo, marine emergency radio, fish finder, live well, navigation lights, interior lights and accessory plugs which are all wired into the group 24 starting battery. I keep thinking I should move most of the accessories to the group 31 as to not drain the starting battery. Note, last year after a couple of hours use my fish finder would give me a low voltage message. That's why I replace the 27 with a 31. How much should I move to the 31, or should I use the 31 as the starting battery. All advice welcomed.

 

[alldodge]

Bought a used boat with a 50 hp motor and two batteries. A group 24 which I thought was for starting, and I replaced the group 27 with a group 31 for all my accessories. It turns out that the only thing being powered by the group 31 is the trolling motor. The boat has a stereo, marine emergency radio, fish finder, live well, navigation lights, interior lights and accessory plugs which are all wired into the group 24 starting battery. I keep thinking I should move most of the accessories to the group 31 as to not drain the starting battery. Note, last year after a couple of hours use my fish finder would give me a low voltage message. That's why I replace the 27 with a 31. How much should I move to the 31, or should I use the 31 as the starting battery. All advice welcomed.

Could be part of your issue could be that your batteries were getting old. I would recommend move the 31 for your starter and get a deep cycle battery for the trolling motor. You could install a battery switch so if your starter did get low you could use the switch to connect both together to restart and get home.

 

[tnq5546]

The group 24 still holds a good charge;13.2 volts when fully charged. The 31 is a dual purpose battery; deep cycle/starting. I thought it would be best to remove the load of the starting battery by moving some of the accessories to the larger battery.

 

[airshot]

Your idea is how my boat is set up. One group 24 marine starting batt is used for starting main engine only and does have a wire for a secondary bilge pump. I also have a group 27 deep cycle that operates all accessories plus the main bilge pump as well as a starting battery for my kicker motor. When trolling the kicker adds a small amount of power back into the battery but otherwise I only put the deep cycle on a charger when it drops to 50/60%. Deep cycle batteries do not like a constant charge according to the mfgs. so I wait until it drops down to the recommended recharge amount. I only troll for the first half of summer then no kicker motor running and the deep cycle will carry me from mid summer until I take it out for the winter which is the first weekend in Nov. I run fish finder, gps, minnow bucket aerator, ship/shore radio, running lights, stero, main bilge pump etc all off deep cycle for 2-3 months without recharge and it still has enough to start the main engine in a pinch if needed. Other then your elec trolling motor which is your biggest elec user, all your other accessories running from your 31 should not be an issue. I believe in having a separate starting battery for my main engine so I don't get hung out to dry.

 

[tnq5546]

That is what I will do. I will keep the trolling motor on the group 31, and add the stereo, emergency radio, fish finder, navigation lights and accessory outlet to this same battery. This way the starting battery can be used primarily for starting. Thanks for the help, sort of new to this, so your assistance is appreciated.

 

[Silvertip]

Or you can do nothing with the wiring and simply carry a small pair of jumper cables. None of the accessories you have are high current draw except perhaps the stereo if it has an external high power amp. The trolling motor is the only high current draw item and it should be on it's own battery. Anything you add to the troller cuts down on run time. Even if both batteries are dead, you can easily rope start a 50 HP motor.

 

[UncleWillie]

The group 24 still holds a good charge;13.2 volts when fully charged. The 31 is a dual purpose battery; deep cycle/starting. I thought it would be best to remove the load of the starting battery by moving some of the accessories to the larger battery.

13+ volts is a false indication from a recently charged battery. 12.6v is the number you want to see.

13.2 volts means the battery is still connected to a maintainer, or was very recently removed from the charger.
After charging, wait a couple of days before measuring the battery voltage.
A good battery will display 12.6v for many weeks to months.
If it drops below 14.4v after a week, it is suspect.

My boat's 4 year old battery was last charged back in October.
It spent the winter on a shelf in the garage.
I just went and measured it. It is still reading 12.56v.

 

[tnq5546]

I left the batteries off the charger for two days. I checked them today and they read 12.8 and 12.9

 

[airshot]

Hmmmm...my deep cycle has not been on a charger for 2 months and reads 12.8 plus volts, during the regular boating season my starting battery typically shows 12.8-13 volts after a week in the barn. I always thought the 12.6 was a minimum voltage on a good battery, as it dropped below it was a sign of a weakening battery.
At least that is how it has been explained to me for years.

 

[UncleWillie]

12 .6 volts is the nominal voltage of a fully charged, Flooded Cell, Lead Acid battery with normal strength Acid at room temperature.
This voltage is determined by the physics of the battery. Lead acid cells are 2.1volts. The 6 cells add up to 12.6.
Lithium cells are nominally 3.7v. and 4.2v when fully charged. 3 cells would deliver 12.6v but fall rapidly to 11.1v.
That is why there are no lithium car batteries available as a simple swap out replacement.

If a battery still reads 12.8 after 2 days, You have one very good battery!
If it still reads 12.8 after 2 months, I would start to question my measurements.
Are these readings with a Quality External Meter, and Not the Boat's Volt meter.

Turn on some lights for a few minutes, or run the Trim up and down.
That will pull off any surface charge quickly and give you a true reading of the battery.